The Science Journal of the American Association for Respiratory Care

2000 OPEN FORUM Abstracts

VALIDATION OF THE CPX EXPRESS GAS EXCHANGE MONITOR DURING MECHANICAL VENTILATION WITH CONTINUOUS BIAS FLOW

Charles McArthur BA RRT RPFT, Immanuel- St.Josephs Hospital / Mayo Health System, Mankato, MN

BACKGROUND: This study was designed to evaluate the ability of a breath by breath gas exchange monitor (CPX Express, Medical Graphics, St. Paul, MN.) to correct for errors introduced by bias flow used during mechanical ventilation.

Methods: A gas exchange validator, which simulates a known VO2, VCO2, and VT, was interfaced with a Puritan-Bennett 840 ventilator (Mallinckrodt, St. Louis, MO.) via a standard patient ventilator circuit. The CPX Express sampled gas concentrations at the proximal end of the patient circuit and expired flow as it exited the ventilator. The ventilator was placed in the CPAP mode to allow delivery of breaths as the validator demanded. Breath by breath measurements of VO2, VCO2, and VT were made at different bias flow settings (set on the ventilator) with the following validator settings: stroke volume 1000 ml, VO2 322 mL/min, VCO2 299 mL/min, frequency 10, duty cycle 0.5. 50 breaths were collected at each bias flow setting.

Results: Measures of agreement (bias ± precision) between the validator and the CPX Express gas exchange monitor are presented below:

BIAS FLOW (L/M) VO2 (%bias ± 2SD VCO2 (%bias ± 2SD VT (%bias ± 2SD)
2 +4.23 ± .38 +1.00 ± .39 -0.76 ± .21
3 -0.33 ± .76 -3.34 ± .74 -5.64 ± .14
6 +4.89 ± 1.85 -3.01 ± 2.15 +1.53 ± .40
9 +1.95 ± 1.90 +1.00 ± 2.22 -2.48 ± .37
12 -1.95 ± 1.74 -1.67 ± 1.25 -4.87 ± .38
15 -2.28 ± 1.14 -2.68 ± .34 -6.21 ± .45
18 -3.91 ± 2.44 -2.34 ± 2.19 -7.64 ± .29

Conclusions: The CPX Express gas exchange monitor can accurately measure breath by breath gas exchange during mechanical ventilation with a continuous bias flow in the range studied.

Partially funded by Medical Graphics Corporation.

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